1. Technical Field
The present invention relates, in general, to an improved wireless communications system. In particular, the present invention relates to a method and system for improving the reliability and success of an attempted call back from a Public Safety Answering Point to a mobile subscriber in the event of a disconnection of an emergency call. Still more particularly, the present invention relates to, in response to a disconnection of an emergency call, automatically disabling termination restrictions of a mobile subscriber unit, at a home location register, for a limited period of time in response to a disconnection of an emergency call originated by the mobile subscriber unit, so that a Public Safety Answering Point is able to call the mobile subscriber unit back.
2. Description of the Related Art
A mobile telephone system typically includes mobile subscriber units that may be mobile or portable, and cellular base stations that are connected to the public telephone company via one or more switching networks. Each mobile subscriber has an assigned cellular telephone number that allows a user to place and receive calls within a widespread range of the cellular base stations, such as throughout a metropolitan area. Mobile telephone subscribers may opt to place certain restrictions, hereinafter termination restrictions, in order to refuse acceptance or to deflect some or all incoming calls. Such termination restrictions include termination denials, toll denials for incoming long distance calls, do-not-disturb restrictions, and call deflections such as call forwarding, call holding, and call waiting. For ease of reference, all types of instructions that interfere with the ability of a mobile subscriber unit to immediately and without delay receive and respond to an incoming call, will be referred to hereinafter as termination restrictions. These termination restrictions are typically implemented as instructions in a home location register (HLR) that serves a mobile subscriber unit (MSU). When a call is sent to a MSU with an applicable termination restriction, a Gateway Mobile Switching Center (G-MSC) is informed by the HLR that the called MSU will not accept the call and the connection will not be made. In the case of a call deflection such as call forwarding, the HLR provides the appropriate destination number which is then utilized to automatically forward the call.
The Emergency Service Bureau (ESB) or more commonly known in the United States as "911" service provides assistance to a person experiencing an emergency. In order to obtain official assistance in case of an emergency, a person may dial a short unique number (such as 911 in the U.S.) to quickly establish a call connection with one of the Public Safety Answering Point (PSAP) terminals providing ESB services. In order to establish the emergency call connection with the PSAP terminal, the directory number associated with the mobile subscriber unit is transmitted to the PSAP. The transmitted directory number or Mobile Station Integrated Service Directory Number (MSISDN, also known as Personal Station Integrated Service Directory Number--PSISDN) is utilized by the PSAP to identify the caller and is also available, if needed, to call back to the mobile subscriber unit if an unintentional disconnect should occur due to lost RF signal, battery failure, etc.
Since it must be assumed that an emergency caller is in dire need of assistance, it is important that every measure be taken to ensure that if the call is unintentionally disconnected, the PSAP may reliably call back the mobile subscriber unit. By utilizing the received MSISDN number, a setup request signal is routed to the Gateway Mobile Switching Center (G-MSC) associated with the destination Public Land Mobile Network (PLMN) which then interrogates the HLR storing subscriber information related to the MSU. The setup request signal is then rerouted to a particular mobile switching center (MSC) currently serving the MSU. However, if an MSU that is utilized to place the emergency call has a termination restriction, the interrogation and rerouting procedures may be ineffective in routing the call from the PSAP to the mobile subscriber unit. The person placing the call is therefore denied effective assistance during an ostensible emergency.
From the foregoing it can be appreciated that a need exists to provide a method and system for automatically disabling termination restrictions of a mobile subscriber unit during an emergency call so that a PSAP terminal can call back to the mobile subscriber unit in the event of an unintentional disconnect.